A growing number of studies
are using specific primary sugar species, such as sugar alcohols or primary saccharides,
as marker compounds to characterize and apportion primary biogenic organic aerosols
(PBOAs) in the atmosphere. To better understand their annual cycles, as well as their
spatiotemporal abundance in terms of concentrations and sources, we conducted a large
study focusing on three major atmospheric primary sugar compounds (i.e., arabitol,
mannitol, and glucose) measured in various environmental conditions for about 5300 filter
samples collected at 28 sites in France. Our results show significant atmospheric
concentrations of polyols (defined here as the sum of arabitol and mannitol) and glucose
at each sampling location, highlighting their ubiquity. Results also confirm that polyols
and glucose are mainly associated with the coarse rather than the fine aerosol mode. At
nearly all sites, atmospheric concentrations of polyols and glucose display a well-marked
seasonal pattern, with maximum concentrations from late spring to early autumn, followed
by an abrupt decrease in late autumn, and a minimum concentration during wintertime. Such
seasonal patterns support biogenic emissions associated with higher biological metabolic
activities (sporulation, growth, etc.) during warmer periods. Results from a previous
comprehensive study using positive matrix factorization (PMF) based on an extended
aerosol chemical composition dataset of up to 130 species for 16 of the same sample
series have also been used in the present work. The polyols-to-PMPBOA ratio
is 0.024±0.010 on average for all sites, with no clear distinction between traffic,
urban, or rural typology. Overall, even if the exact origin of the PBOA source is still
under investigation, it appears to be an important source of particulate matter (PM),
especially during summertime. Results also show that PBOAs are significant sources of
total organic matter (OM) in PM10 (13±4 % on a yearly average, and up to
40 % in some environments in summer) at most of the investigated sites. The mean PBOA
chemical profile is clearly dominated by contribution from OM (78±9 % of the mass
of the PBOA PMF on average), and only a minor contribution from the dust class
(3±4 %), suggesting that ambient polyols are most likely associated with
biological particle emissions (e.g., active spore discharge) rather than soil dust
resuspension.

Airborne particles (or particulate matter, PM) are of major concern due to their multiple
effects on climate and adverse human health impacts (Boucher et al., 2013; Cho et al.,
2005; Ntziachristos et al., 2007). The diversity of PM impacts is closely linked to their
complex and highly variable nature, i.e., size distribution, concentration and chemical
composition, or specific surface properties. PM consists of inorganic and elemental
substances, and a large fraction made of carbonaceous matter (organic carbon, OC, and
elemental carbon, EC) (Franke et al., 2017; Putaud et al., 2004a; Yttri et al., 2007a).
Substantial amounts of atmospheric organic matter (OM) remain unidentified and
uncharacterized at the molecular level. In most studies, a maximum of only 20 % of
particulate OM mass can generally be speciated and quantified (Alfarra et al., 2007;
Fortenberry et al., 2018; Liang et al., 2017; Nozière et al., 2015). This detailed
composition of OM and its spatial and seasonal distribution can give important insights
into the adverse effects of PM. So far, the majority of air pollution studies have
focused on organic atmospheric particles associated with anthropogenic and secondary
sources, whereas a significant fraction of OM can also be associated with primary
emissions from biogenic sources (Bauer et al., 2008a; Jaenicke, 2005; Liang et al.,
2016). Therefore, the characterization of primary OM biogenic sources at the molecular
level is still limited (Fuzzi et al., 2006; Liang et al., 2017; Zhu et al., 2015), and
should be further investigated for a better understanding of aerosol sources and
formation processes.

Primary biogenic organic aerosols (PBOAs) are emitted directly from the biosphere to the
atmosphere where they are ubiquitous and participate in many atmospheric processes
(Elbert et al., 2007; Fröhlich-Nowoisky et al., 2016). Additionally, their inhalation
has long been associated with human respiratory impairments (asthma, aspergillosis, etc.;
Després et al., 2012; Morris et al., 2011). PBOAs comprise living and dead
microorganisms, such as bacteria and fungi; viruses; bacterial and fungal spores;
microbial fragments, such as endotoxins, mycotoxins; or plant materials, such as
vegetative debris and pollens (Elbert et al., 2007; Jaenicke, 2005; Morris et al., 2011).
In most semi-urban European sites, PBOA can account for up to 25 % of the atmospheric
aerosol mass in the size range of 0.2 to 50 µm (Fröhlich-Nowoisky et al.,
2016; Jaenicke, 2005; Huffman et al., 2012; Manninen et al., 2014; Morris et al., 2011).
However, their sources and contribution to total airborne particles are still poorly
documented, partly because of the difficulty to recognize them by conventional
microbiological methods (cell culture, microscopic examination, etc.; Di Filippo et al.,
2013; Heald and Spracklen, 2009; Jia et al., 2010a).

Several specific chemical components, such as primary sugar compounds (i.e., primary
saccharides and sugar alcohols) emitted persistently from biogenic sources, have long
been suggested as powerful and unique biomarkers in tracing sources, as well as
abundances of PBOA (Bauer et al., 2008a; Medeiros et al., 2006; Simoneit et al., 2004b;
Zhang et al., 2010; Zhu et al., 2016). For instance, ambient concentrations of glucose
have been used as markers for plant materials (such as pollen, leaves, and their
fragments) or soil emissions from several areas in the world (Fu et al., 2012; Jia et
al., 2010a, b; Pietrogrande et al., 2014; Rathnayake et al., 2017). Many studies
indicated that glucose is the most abundant monosaccharide in vascular plants, where it
serves as the common energy material, and an important source of carbon for soil active
microorganisms (such as bacteria or fungi) (Jia et al., 2010a; Medeiros et al., 2006;
Pietrogrande et al., 2014; Zhu et al., 2015). Additionally, sugar alcohols (also called
polyols) including arabitol and mannitol have been proposed as markers for airborne
fungi, and are widely used to quantify their contributions to PBOA mass (Bauer et al.,
2008a, b; Golly et al., 2018; Srivastava et al., 2018; Zhang et al., 2010). These sugar
alcohols have also been found to correlate very well with fluorescent PBOA in the
ultraviolet aerodynamic particle sizer (UV-APS) and wideband integrated bioaerosol sensor
(WIBS-3) online studies, particularly in rainy periods (Gosselin et al., 2016), favoring
microbial sporulation (such as fungi belonging to Ascomycota and Basidiomycota phyla)
(China et al., 2016; Elbert et al., 2007; Jones and Harrison, 2004). Polyols are produced
in large amounts by many fungi and bacteria, and several functions have been described
for these compounds, such as common energy storage materials, intracellular protectants
against stressful conditions (e.g., heat or drought), storage or transport of
carbohydrates, quenchers of oxygenated reactive species, or regulators of intracellular
pH by acting as a sink or source of protons (Jennings et al., 1998; Medeiros et al.,
2006; Vélëz et al., 2007). Hence, polyols, especially arabitol and mannitol, may
represent a significant fraction of the dry weight of fungi, and mannitol can contribute
between 20 % and 50 % of the mycelium dry weight (Ruijter et al., 2003;
Vélëz et al., 2007). However, polyols are also often identified in the lower
plants (leaves, pollens) and green algal lichens (Medeiros et al., 2006; Vélëz et
al., 2007; Yang et al., 2012). The primary sugar compounds (defined as polyols and
primary saccharide species) are thought to be relatively stable in the atmosphere (Wang
et al., 2018), although studies investigating their atmospheric lifetime are quite
limited. One previous laboratory study has been conducted by the US Environmental
Protection Agency (EPA) to evaluate the stability of these chemicals on filter material
exposed to gaseous oxidants as well as in aqueous solutions (simulating clouds and fog
droplet chemistry). Findings of that study have shown that primary sugar compounds remain
quite stable up to 7 days (the extent of the testing period), pointing out their
suitability for use as tracers of atmospheric transport (Fraser, 2010). With all of this
information, the use of primary sugar compounds (such as mannitol, arabitol, glucose,
etc.) as suitable tracers of PBOA is generally acknowledged (Jia and Fraser, 2011; Zhu et
al., 2015, 2016).

In this context, the present study was designed to provide a broad overview of the
spatial and seasonal variations in polyols and glucose mass concentrations, as well as
their contribution to the aerosol organic mass fraction in France. To do so, data were
collected at many sites in different environments (rural, traffic, urban) in order to
represent various sampling conditions in terms of site typologies and meteorological
conditions. Thanks to the availability of results from an extended positive matrix
factorization (PMF) analysis performed for the corresponding datasets, the overall
contributions of the main polyols and glucose emission sources could also be investigated
in light of their spatial patterns. To the best of our knowledge, this is the first study
providing such an extended phenomenology of these compounds over multiple sites with
different typologies.

2.1 Aerosol sampling

Ambient aerosol samples considered in the present work come from different research and
monitoring programs, conducted over the last 5 years in France (Fig. 1). Each program
includes at least 1 year of field sampling, providing a total number of 5343 daily filter
samples available for the sake of the present study. These sites offer diverse conditions
in terms of typologies (rural, traffic, urban sites, Alpine valley environments, etc.),
local climate, and vegetation types, and were selected in order to cover the complex and
variable national environmental conditions. These sites are assumed to represent typical
environmental conditions in France, and our observations and general tendency could
therefore be extrapolated to neighboring western European countries presenting quite
homogeneous environmental conditions.

Figure 1Map of sampling site locations in France. Green: rural
background, red: traffic, wheat color: urban background, and dark-wheat color: urban
background in Alpine valley sites. The areas of Grenoble (Grenoble_LF, Grenoble_CB, and
Grenoble_VIF) and Vallée de l'Arve (Marnaz, Passy, and Chamonix) include three sites
each. The area of Marseille includes four sites: Marseille, Mallet, Meyreuil, and
Gardanne.

The site of OPE-ANDRA is a specific monitoring observatory in a rural environment,
without any village or industry within several kilometers (description available from
http://www.andra.fr, last access: 12 February 2019). All
other sites correspond to stations of regional air quality monitoring networks (AASQA).
The availability of filter samples was variable from one site to the other one, depending
on the sampling frequency (typically every third or sixth day). Filter collection was
conducted within the PM10 or the PM2.5 aerosol size fractions, depending on the
investigated site (Table S1 in the Supplement). Moreover, co-located and simultaneous
PM10 and PM2.5 samplings were conducted at OPE-ANDRA and Revin, allowing us to
investigate the distribution of primary sugar compounds between the fine and the coarse
aerosol size fractions at these two sites.

Ambient aerosols were collected onto quartz fiber filters (Tissuquartz PALL QAT-UP 2500,
150 mm diameter) and preheated at 500 ∘C for 4 h minimum before use. After
collection, all filter samples were wrapped in aluminum foils, sealed in zipper plastic
bags, and stored at < 4 ∘C until further chemical analysis. Field blank
filters were also collected, at least once a month, using the same handling procedure as
for PM samples. More detailed information on the sampling periods, air sampler, number of
filters, and nature of PM samples are provided in Table S1 and Fig. S1 in the Supplement.

2.2 Chemical analyses

PM samples were analyzed for various chemical species using subsampled fractions of the
collection filters. In the frame of the present study, the carbonaceous matter (OC and
EC) was analyzed using a thermo-optical method on a Sunset Lab analyzer (Birch and Cary,
1996) as described by Aymoz et al. (2007) using the EUSAAR2 temperature program (Cavalli
et al., 2010), except for the five sites of northern France where the NIOSH870 protocol
was employed (Birch and Cary, 1996). OM contents were then estimated by multiplying the
organic carbon mass concentrations by a fixed factor, with OM=1.8×OC. This OM-to-OC ratio value of 1.8 was chosen based on previous studies
performed in France (Favez et al., 2010; Petit et al., 2015, and reference therein) and
around the world. (e.g., Aiken et al., 2008; Li et al., 2018; Ruthenburg et al., 2014;
Vlachou et al., 2018), with a typical range of 1.2–2.4 for these values.

For the analysis of anhydrosugars, sugar alcohols, and primary saccharides, filter
punches (typically of about 10 cm2) were first extracted into ultrapure water, then
filtered using a 0.22 µm Acrodisc filter. Depending on the site, analyses were
conducted either by the IGE (Institut des Géosciences de l'Environnement) or by the
LSCE (Laboratoire des Sciences du Climat et de l'Environnement) (Table S1). At IGE,
extraction was performed during 20 min in a vortex shaker and analyses were achieved
using high-performance liquid chromatography (HPLC) with pulsed amperometric detection. A
first set of equipment was used until March 2016, consisting of a Dionex DX500 equipped
with three columns (Metrosep Carb 1-Guard + A Supp 15–150 + Carb 1–150); the
analytical run being isocratic with 70 mM sodium hydroxide eluent, followed by a
gradient cleaning step with a 120 mM NaOH eluent. This analytical technique enables us
to detect anhydrous saccharides (levoglucosan, mannosan, galactosan), polyols (arabitol,
sorbitol, mannitol), and glucose (Waked et al., 2014). A second set of equipment was used
after March 2016, with a Thermo Fisher ICS 5000+ HPLC equipped with 4 mm diameter
Metrosep Carb 2×150 mm column and 50 mm pre-column. The analytical run is
isocratic with 15 % of an eluent of sodium hydroxide (200 mM) and sodium acetate
(4 mM) and 85 % water at 1 mL min−1. This method allows for additional
separation and quantification of erythritol, xylitol, and trehalose. At LSCE, extraction
was performed during 45 min by sonication and analyses were achieved using an ion
chromatography (IC) instrument (DX600, Dionex) with pulsed amperometric detection
(ICS3000, Dionex). A CarboPAC MA1 column was used (4×250 mm, Dionex), the
analytical run being isocratic with 480 mM sodium hydroxide eluent. This analytical
technique enables us to detect anhydrous saccharides (levoglucosan, mannosan,
galactosan), polyols (arabitol, mannitol), and glucose.

Field blank filters were handled as real samples for quality assurance. The present data
were corrected with field blanks. The reproducibility of the analysis of primary sugar
species (polyols, glucose), estimated from the analysis of extracts of 10 punches from
the same filters, is generally in the range of 10 %–15 %.

Additional chemical analyses were conducted for most of the sites, allowing us to
quantify up to 130 different chemical species (Calas et al., 2018). Then 30–35 chemical
species were selected in order to achieve PMF analyses as discussed hereafter.

2.3 Statistical analysis

Species concentration measurements were first analyzed for normality using
Shapiro–Wilk's method with the statistical program R studio interface
(version 3.4.1). Since data were generally not distributed normally, we used
nonparametric statistical methods. The strength of the relationship between species
concentrations was investigated using the nonparametric Spearman rank correlation method.
Multiple mean comparison analyses were performed with the Kruskal–Wallis test method.
Statistical significance was set at p< 0.05.

Positive matrix factorization for the source apportionment of the PM was previously
performed at several sites of this study, as part of the SOURCES (Favez et al., 2016) and DECOMBIO (Chevrier, 2017) projects. We used the US EPA PMF 5.0
software (US EPA, 2015), following the general recommendation guidelines of the European
Joint Research Centre (JRC; Belis et al., 2014). Briefly, the SOURCES program aimed at
performing source apportionment at 15 sites using a harmonized methodology, i.e., using
the same chemical species, uncertainties, constraints, and criteria for factor
identification. The PMF conducted within the SOURCES project uses about 30 different
species (Table S6), including carbonaceous fraction (OC, EC), ions (Cl−,
NO3-, SO42-, NH4+K+, Mg2+,
Ca2+), organic markers (polyols, i.e., sum of arabitol, mannitol, and sorbitol;
levoglucosan; mannosan), and metals (Al, As, Ba, Cd, Co, Cs, Cu, Fe, La, Mn, Mo, Ni, Pb,
Rb, Sb, Se, Sn, Sr, Ti, V, Zn). The PMF conducted within the DECOMBIO project, for the
sites of Marnaz, Chamonix, and Passy, used aethalometer (AE 33) measurements instead of
EC measurements (Chevrier, 2016). This complementary measure gives the total black carbon
(BC), thus enabling the deconvolution of BC concentrations into its two main
constituents: wood-burning BC (BCwb) and fossil-fuel BC (BCff)
(Sandradewi et al., 2008). For graphical simplicity, BCwb and
BCff were summed up and labeled as EC in the following figures. PMF modeling
was performed separately for each site. Statistical significance was validated with
bootstrapping higher than 80 % for each factor. Detailed methodology and results
about these studies are given in their respective papers (Chevrier, 2017; Favez et al.,
2016). It should be noted that glucose was not included in the
final solution for any of these PMF, since it generally produced statistical instability
of the solutions (this point is further discussed in Sect. 3.2).

The PMF analysis took advantage of the ME-2 algorithm to add constraints to
different chemical profiles (see Tables S3 and S4 for details). Mainly soft
constraints were applied in order to add some prior knowledge about the
emission sources and “clean” the different profiles without forcing the
model toward an explicit solution. In particular, the polyol concentrations
were “pulled up maximally”, while levoglucosan and mannosan were set to
zero, and EC was “pulled down maximally” in the PBOA factor. This was
achieved to avoid mixing with the biomass burning factor as well as possible
influences of unrealistic high contributions of EC to PBOA. Other constraints
were added parsimoniously to other factors, targeting specific proxies of
sources (Table S4).

As for the general results of this large PMF study, we identified some well-known sources
for almost all the sites (biomass burning, road traffic, secondary inorganics, dust and
sea salt). Two other less-common factors were identified for all sites: secondary
biogenic aerosols (probably from marine origin), traced mainly by the presence of methanesulfonic acid (MSA), and PBOA, traced by the presence of more than 90 % of the
polyols total mass in the factor. Table S5 and Fig. S4 present a more detailed
description of the chemical tracers in each factor, together with their yearly average
contribution for each site. Hereafter, only the PBOA chemical profile will be extensively
investigated. The uncertainties in this PBOA factor are discussed below and its stability
is presented in Fig. S5. Bootstrap analysis based on 100 resampling runs evidenced the
very high stability of this PBOA factor since the PBOA initial constrained factor was
mapped to the PBOA bootstrap factor more than 99 % of the time.

3.1 Relative distribution between sugar alcohols and glucose

Figure 2 presents an overview of the relative mass concentration distributions of
individual chemical species quantified at two sites with very different characteristics,
an urban site in Grenoble and the rural site of OPE-ANDRA. Data are presented for the
warmer season (e.g., during summer and fall), when concentrations were at their maximum
(see Sect. 3.4). Glucose is the most abundant species measured (average
37.6±26.4 ng m−3), accounting on average for 25 % of primary sugar
compounds (SC) total mass at both sites. Mannitol (37.3±24.6 ng m−3) and
arabitol (32.0±22.2 ng m−3) are the second and third most abundant species,
accounting for 25 % and 23 % of SC mass, respectively. Trehalose is relatively
abundant in samples from these two sites (20.1±16.2 ng m−3), accounting for
14 % of SC mass, but in general its concentration is frequently below the limit of
quantification for samples from other sites in France. The other identified polyols
(i.e., erythritol, inositol, glycerol, sorbitol, and xylitol) present lower concentration
levels (4.9±2.1 ng m−3), corresponding altogether to 13 % of SC total
mass.

Such ambient mass concentration distribution patterns are similar (but with variable
intensities) to those previously reported for aerosol samples collected at various
locations around the world. For example, Verma et al. (2018) found that glucose, and
arabitol together with mannitol, contributed to 16.7 % and 48.1 %, respectively,
of total primary sugar compounds in aerosols from Chichijima island. Similarly, Yttri et
al. (2007b) showed that glucose and the pair arabitol and mannitol were the main
contributors of total primary monosaccharides and sugar alcohols in aerosols collected
from four various background sites in Norway. In addition, Carvalho et al. (2003)
reported that arabitol, mannitol, and glucose are the most dominant primary sugar
compounds in aerosols from rural background and boreal forest sites in Germany and
Finland, respectively.

Although various primary sugar alcohols and saccharides have been detected and quantified
for most of the investigated sites, the following study focuses only on the three major
and ubiquitous species, namely arabitol, mannitol, and glucose. Figure 3 presents their
average relative contributions at all sites, for the warmer period, displaying very
similar features at a first glance. However, discrepancies could be observed from site to
site, as discussed in the following sections.

3.2 Relationships between selected primary sugar compounds

Figure 4 summarizes linear correlations obtained between arabitol and mannitol
concentrations at each site during the warmer period. Medium to very high coefficients of
determination could be observed (0.58≤R2≤0.93; 30≤n≤143 or 45≤n≤341 for PM2.5 and PM10 series, respectively), with slopes in a
rather narrow range (between 0.59 and 1.10), and quite low intercepts (always below
9 ng m−3). Such covariations indicate that both species are most probably
co-emitted, by one or several type(s) of sources, at each site during the summer–autumn
period. These observations are in agreement with previous studies also showing strong
covariations between arabitol and mannitol (Kang et al., 2018; Verma et al., 2018; Zhu et
al., 2015). Therefore, it seemed reasonable to consider both species together so that
their concentrations are summed up and labeled as “polyols” in the following sections.

Figure 4Linear regression analysis between selected primary sugar compound mass
concentrations (i.e., arabitol, mannitol, and glucose) during summer and autumn seasons
(June to November) for all the sites considered in this study.

Conversely, linear correlations between glucose and polyol concentrations are generally
weaker (0.10<R2≤0.78), with slopes varying over a much larger range
(between 0.12 and 0.94), and variable intercepts (between −5.6 and 16.4 ng m−3).
This suggests that glucose concentrations might follow a different pattern compared to
that of polyols, either due to different emission sources, or different chemical
stability in the atmosphere. It is therefore reasonable to keep glucose as a separate
chemical species in the following discussion.

It should be emphasized that the variability in the slope of the regressions
between the chemical concentrations is most probably related to the emissions
and atmospheric processing. Particularly in the case of mannitol and
arabitol, they may be influenced by biogenic or biotope characteristics.
Nevertheless, no evident relationship between the slope values and the
typology or the geographical location of the sites could be observed
(Fig. 4).

3.3 Relative distributions between PM10 and PM2.5

Figure 5 shows the average PM10 and PM2.5 concentrations of polyols and glucose
at OPE-ANDRA and Revin during the summer and autumn seasons. The polyol mass
concentrations ranged from 7.5±10.9 to 27.8±33.3 ng m−3 in PM2.5, and
from 48.9±38.2 to 73.5±61.8 ng m−3 in PM10, in Revin and OPE-ANDRA
sites, respectively. PM10-to-PM2.5 ratios were then on average of about 3 to 5.
Similar size distribution patterns, with variable intensity, were observed for glucose
(Fig. 5). These results indicate that polyols and glucose are mainly associated with the
coarse PM fraction. This observation is in good agreement with several previous
investigations where polyols (especially arabitol and mannitol), together with glucose,
were prevalent in the coarse fraction (Fu et al., 2012; Fuzzi et al., 2007; Pio et al.,
2008; Yttri et al., 2007b). However, Carvalho et al. (2003) reported different size
distributions for polyols and glucose, with variable fine or coarse mode maxima depending
upon sampling location. For instance, maximum atmospheric concentrations of mannitol were
associated to fine and coarse aerosols from boreal forest (Finland) and rural background
sites (Germany), respectively. The authors hypothesized that these observations are due
to different assemblages of dominant fungal biota (with variable aerodynamic
characteristics) at different sites. Some other previous studies showed aerodynamic
diameters typically ranging from 2 to 10 µm, even though a few airborne
bacterial/fungal spores could exceed that size (Bauer et al., 2008a; Elbert et al., 2007;
Huffman et al., 2012; Zhang et al., 2015).

Figure 5Box plots of mass concentrations of polyols (a) and glucose
(b) in PM10 and PM2.5 (with symbol * samples). Black markers inside
each box indicate the mean concentration value, while the top, middle, and bottom lines
of the box represent the 75th, median, and 25th percentile, respectively. The whiskers at
the top and bottom of the box extend from the 95th to the 5th percentile. The number of
samples was N= 123 for OPE-ANDRA and N= 87 for Revin. Statistical
differences between average mass concentrations were analyzed with the Kruskal–Wallis
methods (p<0.05).

Hence, although the precise mechanisms of atmospheric emission of particulate polyols and
glucose are not fully resolved, our observations are in good agreement with ambient mass
concentrations of polyols and glucose being likely associated with biological particles,
as already suggested elsewhere (Fu et al., 2012; Verma et al., 2018; Zhang et al., 2015).
These species could enter into the atmosphere through either natural or anthropogenic
resuspension of surface soils and associated bacterial/fungal spores (containing polyols
and primary sugar compounds), or via a direct input resulting from microbial activities
(e.g., sporulation). Another hypothesis would be the abrasion of leaves and the
subsequent release of microbial organisms and plant debris (Fu et al., 2012; Medeiros et
al., 2006; Simoneit et al., 2004b).

Figure 6Spatial and seasonal distributions of atmospheric polyol average concentrations
(ng m−3) for various types of sites in France. Error bars correspond to standard
deviations calculated with seasonal concentrations. Years of PM sampling campaigns are
not concurrent at all sites (see Fig. S1). The seasons were defined as follows: Winter is
December to February, Spring is March to May, Summer is June to August, and Autumn is
September to November.

3.4 Spatial and seasonal distribution of atmospheric concentrations

3.4.1 Spatial and seasonal patterns of polyol concentrations

As illustrated in Fig. 6, significant concentrations of polyols were measured at each
investigated site, evidencing the ubiquity of these organic compounds. The annual average
concentration levels of polyols measured in PM10 aerosols at all sites
(33.2±33.5 ng m−3; see Table S2) are within the range previously reported for
urban and rural sites across Europe (Burshtein et al., 2011; Di Filippo et al., 2013;
Pietrogrande et al., 2014; Yttri et al., 2007b, 2011). Additionally, polyol mass
concentrations clearly exhibit seasonal trends, with variable intensity according to the
sampling sites. On a seasonal average, polyols are more abundant in summer
(46.8±43.6 ng m−3) and autumn (43.0±36.7 ng m−3), followed by
spring (19.0±13.6 ng m−3) and winter (16.2±11.5 ng m−3). The
average concentrations of polyols are at least 2 to 3 times higher during summer or
autumn months than during the cold months, with a ratio that can be as high as 8 to 10.

Previous studies also reported a similar seasonal variation pattern for urban and rural
aerosol samples collected at various locations. For example, Pashynska et al. (2002)
measured higher atmospheric polyol (arabitol, mannitol) contents during late summer and
autumn in Belgium. Several other studies reported higher concentrations of polyols in
summer than in spring and winter time in aerosols collected from Texas, USA, and Jeju
island, South Korea, respectively (Fu et al., 2012; Jia et al., 2010a, b). More recently,
Liang et al. (2016) and Verma et al. (2018) also reported similar seasonal distributions
for aerosols sampled in Beijing, China, and the northwestern Pacific, respectively.

The higher atmospheric polyol concentrations observed are likely due to the increased
contribution from metabolically active microbial-derived sources (fungi, bacteria, green
algal lichens) as a result of external stressors such as heat, drought, and relative
moisture. Indeed, fungal and prokaryotic cell activities, including their growth and
sporulation, are promoted by high temperature and humid conditions occurring in summer
and autumn (China et al., 2016; Elbert et al., 2007b; Jones and Harrison, 2004;
Rathnayake et al., 2017).

As also evidenced from Fig. 6 that atmospheric polyol concentrations do not present any
significant seasonal differences related to the site typology (rural, traffic, urban
sites with/without Alpine influences) or latitude. There is some tendency toward higher
concentrations in summer in Alpine environments, but some other sites (like the rural
site of OPE-ANDRA in the northeast of France) can reach the same levels of
concentrations. We tested several types of hierarchical classifications, including
variables like monthly or seasonal mean polyol concentrations, the arabitol-to-mannitol
ratio, or linear regression parameters (slope, R square) but none of them led to a
simple clustering of the sites that would explain the variability of the concentrations.

3.4.2 Spatial and seasonal patterns of glucose concentrations

The annual average concentrations of glucose measured in PM10 aerosols at all sites
(20.4±15.6 ng m−3; see Table S2) are comparable to those previously reported
for various sites across Europe (Alves et al., 2006; Theodosi et al., 2018; Yttri et al.,
2007b, 2011). Like polyols, the atmospheric concentrations of glucose also display
seasonal and site-to-site variations (Fig. 7). The ambient seasonal mean concentrations
(with standard deviations) of glucose are maximum in summer (25.0±24.2 ng m−3)
and autumn (24.6±19.8 ng m−3), followed by spring
(15.8±12.4 ng m−3) and winter (12.6±10.2 ng m−3). The summer to
winter ratio for glucose seems generally lower than that of polyols, with higher ratios
in the Alpine areas than in other parts of France. However, as for polyols, it remains
difficult to classify the sites according to any criteria linked to site typology or
latitude.

Figure 7Spatial and seasonal distributions of atmospheric glucose levels (ng m−3)
for various types of sites in France (except the site of Nogent, which presented too many
missing values). Error bars correspond to standard deviations calculated with seasonal
concentrations.

The seasonal trend of glucose concentrations in the present work is similar to that
recently observed for aerosols (PM10 or total suspended particles) collected at
various environmental background (suburban, urban, and coastal) sites around the world
(Liang et al., 2016; Srithawirat and Brimblecombe, 2015; Verma et al., 2018). On average,
a wide range of daily glucose concentrations (expressed as min–max, mean) in PM10
(0.1–297.2 ng m−3, 20.4±15.6 ng m−3) were observed in the present
study. These values are comparable to those in PM10 (8.4–93.0, 47.0 ng m−3)
reported from an urban site in Norway (Yttri et al., 2007b). More recently, Liang et
al. (2016) also reported similar concentrations in PM10 (3.1–343.6,
46.2±27.5 ng m−3) from Beijing (China).

The sources and formation processes of glucose in the atmosphere are not currently well
known and are rarely discussed. Glucose is an important carbon source for metabolically
active soil microbiota, and it is commonly present in vascular plants. Additionally,
cellulose (a linear polymer made of glucose subunits linked by β-1,4 bonds) is one
of the most important form of organic compounds in terrestrial ecosystems and a major
plant structural polymer (Boex-Fontvieille et al., 2014). It can also be quite abundant
in the atmosphere (Puxbaum and Tenze-Kunit, 2003). Hence, it is hypothesized that ambient
glucose could be formed through active microbial (bacteria, fungi, etc.) enzymatic
hydrolysis of cellulose in plant debris. Consistent with these observations, glucose
could be released into the atmosphere from both vascular plant materials (leaves, fruits,
pollens, etc.) growing in spring and decomposing in autumn/summer and soil microbiota, as
already suggested elsewhere (Di Filippo et al., 2013; Jia et al., 2010a; Medeiros et al.,
2006; Verma et al., 2018; Zhu et al., 2015).

Figure 8Spatial and seasonal distributions of mean contributions (in %)
of polyols to the organic matter content of PM for various types of sites in
France. Daily time series of organic carbon (OC) were not available for the
following sites: Gardanne, Mallet, and Meyreuil. Error bars correspond to
standard deviations calculated with seasonal concentrations.

3.4.3 Relative contributions to aerosol organic matter concentrations

The average contribution of polyols to the OM content of PM clearly displayed a seasonal
behavior, as shown in Fig. 8. Here again, contributions are 2 to 10 times higher during
summer and autumn compared to winter and spring, consistent with the assumption of higher
emissions during these periods. The seasonal mean contribution of polyols to OM
fluctuates from site to site and accounts for 0.1 % to 2.1 % of overall OM for
these French sites (Fig. 8). Similarly, the seasonal mean concentrations of polyols
together with glucose represent between 0.2 % and 3.1 % of total OM at these
sites (Fig. S2). However, on a daily basis (Samake et al., 2018), atmospheric polyol mass
concentrations can represent up to 6.3 % of total OM in PM10, indicating that
polyols can be amongst the major molecular species identified in aerosol organic matter
(Fig. S3). Again, we could not find any simple way to group the sites according to their
characteristics (typology or latitude, or climatic region) in order to better understand
the drivers behind the variability in this mass fraction. Further studies are currently
being conducted using multi-criterion examinations.

The seasonal polyols-to-OM distribution patterns in this study are comparable to those
found for different urban or rural sites in Europe (around 0.2 % to 2.5 % of OM;
Pashynska et al., 2002; Yttri et al., 2007b). Zhu et al. (2015) also reported a similar
seasonal polyols-to-OM contribution trend for aerosols sampled at Cape Hedo (coastal
site, Japan).

3.5 Primary biogenic factor in PMF studies

The sum of polyols (arabitol + mannitol) represents only a small fraction of the
total OM. However, as proxies of PBOA, they are most probably emitted with other chemical
species. Emission from biological particles is a complex topic since it may include a
wide variety of compounds, both organic and inorganic (Elbert et al., 2007; Zhang et al.,
2015). Moreover, it is not clear if polyols are mainly emitted directly in the atmosphere
or are linked to other materials, e.g., with soil dust during resuspension processes. To
investigate the relationship between polyols and other molecular tracers of emission
sources, it is possible to perform simple correlation analysis with individual chemical
species. This approach has the disadvantage of being a one-to-one relation and thus
highly sensitive to the dynamics of all PM emission sources, not only the one we are
interested in. Alternatively, another way is to use a PMF approach, also based on
correlations but including much more information on the temporal variations of the
different sources influencing the PM chemistry at a given receptor site.

As mentioned in Sect. 2.3, the PMF results used in this study include sites of different
typologies (rural, traffic, urban sites in Alpine valley environments, etc.) for 16
different locations spread over France and part of the current dataset. At each site, the
PMF studies allowed us to identify a PBOA factor, characterized by the presence of more
than 90 % of the total polyol content (sum of arabitol, mannitol, and sorbitol), as
presented in Table S5 and Fig. S6. Moreover, the sensitivity of this factor to random
noise in the data was investigated thanks to randomly resampling the input matrix of
observation. In PMF analysis, this is done via the bootstrap method (Paatero et al.,
2014) in the constrained run. The PBOA factor was always mapped to itself for 13 of the
sites and nearly always (97 %) for the last three ones. It means that the PBOA factor
does have a very high statistical stability since it never swaps with another factor (see
Fig. S5). Hence, the chemical composition of this factor may be informative to
investigate the PBOA source components (Table S6), and to evaluate the importance of PBOA
emissions in terms of OM mass apportionment.

3.5.1 Contributions of PBOA to OM and polyols to PBOA

Altogether, the results from the 16 sites highlight the importance of the PBOA source
contribution to total OM. As shown in Fig. 9, the OM apportioned by the PBOA factor
represents a significant fraction of the total OM mass on a yearly average (range
6 %–28 %; average 13±6 %). When considering only the summer period
(June–July–August), this contribution is even larger and can exceed 40 % of the
total OM at sites in the Alpine area (Marnaz, Passy, Chamonix, Grenoble_LF), which are
partially protected from large regional influences due to the local topography. This
result may be nuanced, in particular during summer, since some extent of mixing between
PBOA and biogenic secondary organic aerosols (BSOAs) cannot be entirely excluded.
However, several evidences tend in favor of a nonsignificant mixing between BSOA and
PBOA. First, the ratio of polyols-to-OCPBOA shows a low variability from site
to site, while it is unlikely that such a secondary process led to the same amount of OC
for all sites since they present different meteorology, sunshine duration, etc. Second,
the bootstrap analysis does not show any “swap” between factors for the PBOA profile
for all sites, indicative of a well-defined factor (see Fig. S5). Finally, the
OCPBOA-to-polyols ratio in this work (about 16) is in the range expected for
fungal spores (12–27, when arabitol and mannitol are considered together) (Bauer et al.,
2008a; Yttri et al., 2011).

Figure 9Mass contribution of polyols to OM in the PBOA factor, and relative
contributions of the OMPBOA factor to the total OM in PM for the 16 studied
sites where the PMF model was run, over the year and summertime only. Stars and circles
refer to urban sites without and with Alpine valley influence, respectively. Pentagons
correspond to traffic sites and diamonds to rural sites.

Interestingly, some previous work using the same samples from the sites in the Arve
valley (Passy, Chamonix) showed that about 90 % of the OM is from modern origin
(using 14C measurements) during summer, with no apparent correlation between this
modern carbon and polyol concentrations (Bonvalot et al., 2016). Hence, despite being an
important contributing source, PBOA is not the major biogenic source in this type of
environment.

Interestingly, opposite to the case of the Alpine valleys where this proportion is the
highest, the ratios OMPBOA-to-OMtot are amongst the lowest for coastal
environments (Talence, Marseille, Nice), a possible indication that the marine
environment is not a large emitter for these species. Recently, much lower concentrations
of polyols in aerosols from marine environments than those in terrestrially influenced
sites were also reported off the coast of Japan, also suggesting a higher contribution
from terrestrial sources (Kang et al., 2018).

As illustrated in Fig. 9, polyols represent only a small fraction of the OM apportioned
in the PBOA factor (1.2 %–6.0 %; average 3.0±1.5 %) for the 16 studied
sites. This variability is indeed rather small, considering the wide range of sites and
the diversity of other potential sources (on average 8 to 10 PMF factors were obtained
for the different sites). Indeed, this narrow range of the polyol fraction to the
OMPBOA highlights the stability of the chemical profile of this source over a
large regional scale. It indicates also that, if polyols are good proxies of the PBOA
sources, a large amount of other organic species are co-emitted, which still remain
unknown.

Figure 10PMF chemical profile of the PBOA factor in the DECOMBIO and SOURCES programs
expressed as a fraction of the PM mass. Values lower than a few pg µg−1
are not displayed on purpose. For each box, the top, middle, and bottom lines represent
the 75th, median, and 25th percentile, respectively. The whiskers at the top and bottom
of the box extend from the maximum to the minimum. OC* corresponds to the bulk organic
carbon fraction minus the carbon in the characterized organic species. MSA is methanesulfonic acid.

3.5.2 PBOA profile constituents and emission process

Figure 10 shows the contribution (in micrograms of species per micrograms of PM in the
PBOA factor profile) of each chemical species included in the averaged PBOA factor from
the 16 PMF studies. The principal contributors are OC and EC, and significant fractions
of crustal material also appear (Na+, K+, Ca2+, Al, Ba, Cu,
Fe, Mn, Ti, Zn) as well as secondary contributors such as nitrate and sulfate. However,
EC appears to be highly variable both within and between sites under consideration. The
reader may refer to Fig. S7 for an estimation of the EC mass uncertainties at the
different sites. On average, the PBOA factor does not comprise a large fraction of metals
and trace elements, most of them being below 1 pg µg−1. Here again, the
low variability in the PBOA chemical profile encountered across a large array of sites is
remarkable.

The contribution from some crustal material could agree with the coarse mode
distributions of polyols (Sect. 3.3) and could be indicative of an emission process with
the entrainment of spores with soil dust resuspension. To investigate the importance of
mineral dust in the PBOA factor, we clustered the chemical components of PM from PBOA
into seven classes: OM (= 1.8 × OC), EC, NO3-,
NH4+, non-sea-salt sulfate (nss-SO4), sea-salt, and dust. The
nss-SO42- is calculated from the measured SO42- minus the
sea-salt fraction of SO42-
(nss-SO42-=SO42--ssSO42- where ssSO42-=0.252×Na+)
according to Seinfeld and Pandis (1997). The sea-salt fraction is calculated according to
Putaud et al. (2010): sea-salt =Cl-+1.47×Na+. Finally
the dust fraction is estimated thanks to Putaud et al. (2004b) as
dust =(nss-Ca2+)×5.6 with nss-Ca2+ meaning non-sea
salt Ca2+ and is computed thanks to nss-Ca2+=Ca2+-Na+/26. We note that the conversion coefficient provided
by Putaud et al. (2004b) may be influenced by an extreme value and then gives only a low
estimate of dust resuspension.

Figure 11Average contribution (%) of species in the PBOA factor for the
sites in SOURCES and DECOMBIO. The hatched area represents the proportion of
the OM apportioned by the polyols (see text for reconstruction method).

Figure 11 presents the normalized average contributions of these seven classes to the
PBOA mass for the 16 sites with PMF modeling. It clearly reveals that the PBOA factor is
dominated by contributions from OM (78±9 %), followed by EC (9±7 %), and
only a minor contribution from the dust class (3±4 %).

The large value for the contribution of EC is driven by two high values obtained at the
sites of Strasbourg (that reaches 25 %) and Chamonix (18 %) both influenced by
direct and indirect traffic emissions. However, six other sites present no EC in PBOA.
Moreover, the uncertainties of EC in the PBOA profile of Strasbourg and Chamonix is
rather high (between 5 % and 30 % of PM mass at Strasbourg, see Fig. S7). On a
yearly average, EC apportioned by this factor (0 to 400 ng m−3 depending on the
site) is close to the rural EC background in France of about 300 ng m−3 (Golly et
al., 2018).

This result on the general chemical profile of the PBOA factor, with a low crustal
fraction, tends to invalidate the hypothesis of an emission process associating PBOA
material with mineral dust resuspension. Indeed, our findings rather suggest that a main
part of PBOA (and polyols) is most likely associated with direct biological particle
emissions. It leaves only a minor fraction that could be linked to the mechanical
resuspension of PBOA with crustal elements. Some minor fraction of EC in this factor
could come from resuspended EC-containing dust particles being accumulated in topsoil as
demonstrated in previous works (Forbes et al., 2006; Hammes et al., 2007; Zhan et al.,
2016). Hence, the origin of the larger fraction of the contribution of EC remains
unknown. Our conclusions are in good agreement with those made by Jia and Fraser (2011),
based on the concentrations of these chemicals in different types of samples, i.e.,
size-fractionated (equivalent to PM2.5 and PM10) soil, plant, fungi, and
atmospheric PM2.5 and PM10. They found that the ambient concentrations of
primary saccharide compounds at the suburban site of Higley (USA) are typically dominated
by contributions of biological materials rather than resuspension of soil dust particles
and associated microbiota.

The contribution of primary biogenic organic aerosols to PM is barely documented in the
scientific literature. The present study aimed at providing a broad overview of the
spatial and temporal evolution of concentrations and contributions to aerosol organic
matter (OM) of dominant primary sugar alcohols and saccharide compounds for a broad
selection of environmental conditions in France. With 28 sites and more than
5340 samples, it is, to our knowledge, the most comprehensive dataset for these
compounds. The main results obtained indicate the following:

Among the identified polyols, arabitol together with mannitol are the major
species by mass, with lesser amounts of other polyols (e.g., erythritol, inositol,
glycerol, sorbitol, and xylitol). Glucose is the dominant primary monosaccharide and its
relative abundance is comparable to the sum of arabitol and mannitol.

The two main polyols (arabitol and mannitol) together with glucose are
mainly present within the coarse aerosol mode.

At nearly all sites, ambient levels of the main polyols and glucose
displayed clear seasonal variation cycles, with a gradual increase from
spring and maximum in summer and autumn aerosols, followed by a sudden
decrease in late autumn, and a winter minimum.

Atmospheric concentrations of the main polyols and glucose fluctuate
according to site and season, and account each for between 0.1 % and
2.1 % of OM on a seasonal average basis at these French sites.

Ambient mass concentrations of arabitol and mannitol are comparable.
Meanwhile, they display very good temporal covariation, with ratios varying between
sites. Conversely, linear correlations between the main polyols and glucose
concentrations are much lower, suggesting different atmospheric sources or atmospheric
processes.

Arabitol and mannitol are efficient organic markers for PBOA. PMF studies of
the yearly series from 16 sites give contributions of the primary biogenic emission
(traced with the main polyols) to the total OM around 13±6 % on a yearly average
and 26±12 % during summer, thereby showing that PBOA is an important source of
total OM in PM10 for all sites across France. Furthermore, the average PBOA chemical
source profile is made up of a very large fraction of OM (78±9 % of the total
PBOA mass on average), suggesting it is mainly related to direct biogenic emissions from
biological particles. Note that the presence of BSOA within the PBOA factor, particularly
during summer, could not be fully ruled out and further research using additional organic
tracers (such as 3-methylbutanecarboxylic acid, pinic acid, and/or cellulose) are still
needed to solve this issue. Additionally, the low crustal fraction indicates that this
factor is weakly linked to soil dust resuspension associated with biological material.

However, the PBOA source remains chemically poorly characterized as the main
polyols represent only a small fraction of its total OM mass
(3.0±1.5 % on average).

Despite comparable high concentrations in the atmosphere, the sources and
processes leading to glucose concentrations and seasonal evolutions are still elusive.
Indeed, the different PMF performed with glucose as input variable do not lead to a
statistically stable solution.

Further investigations of the emission pathways and chemical characterization of the PBOA
source associated with polyols are ongoing, which may improve our understanding of the
dynamics at various geographical scales for a potential implementation in emission models
in the future.

JLJ was the supervisor for the PhDs of AS,
FC, and SW, and for the postdoc of DS. He directed all personnel who performed the
analysis at IGE. He was coordinator or principal investigator (PI) of the programs that
generated the data for 18 of the 28 sites in this study (OPE-ANDRA, Part'Aera, CAMERA,
SRN 2013, 3 Villes PACA, DECOMBIO, QAMECS) and co-PI for programs for five other sites.
He is the coordinator for the CNRS LEFE-EC2CO CAREMBIOS program that is funding the work
of AS. GU was the co-supervisor for the PhD of AS and SW. OF is the coordinator of the
CARA program, (co-)funding and supervising the filter sampling and chemical analyses at
12 of the 28 sites. EP, OF, and VR supervised the PhD of DMO who investigated the five
sites in northern France. Finally, JLB was the coordinator (program Lanslebourg) or
partner of several programs whose data were used in this study (OPE-ANDRA, Part'Aera,
3 Villes PACA, DECOMBIO), and OF was the coordinator of the SOURCES program, which
includes the work of DS as a postdoctoral fellow under the supervision of JLJ to gather
and prepare most of the datasets used in the present study.

All authors from the ANDRA (author affiliation no. 6) and AASQA (author affiliation nos. 7 to
14) are
representatives for each network that conducted the sample collection and the general
supervision of the sampling sites.

FC and DS ran the PMF analysis. AS, SW, and JLJ processed the data and wrote the
manuscript. All authors reviewed and commented on the manuscript.

The PhD of Abdoulaye Samaké and Samuël Weber are funded by the Government
of Mali and ENS Paris, respectively. We gratefully acknowledge the LEFE-CHAT
and EC2CO programs of the CNRS for financial supports of the CAREMBIOS
multidisciplinary project. Samples were collected and analyzed in the frame
of many different programs funded by ADEME, Primequal, the French Ministry of
Environment, the program CARA led by the French Reference Laboratory for Air
Quality Monitoring (LCSQA), and actions funded by many AASQA, ANDRA, IMT
Lille Douai (especially Labex CaPPA ANR-11-LABX-0005-01 and CPER CLIMIBIO)
projects. Analytical aspects were supported at IGE by the Air-O-Sol platform
within Labex OSUG@2020 (ANR10 LABX56). We acknowledge the work of many
engineers in the lab at IGE for the analyses (Aude Wack, Céline Charlet,
Fany Donaz, Fany Masson, Sylvie Ngo, Vincent Lucaire, and Anthony Vella), as
well as Bruno Malet and Laurent Y Alleman. (IMT Lille Douai) for analyzing
trace and major elements in aerosols from the northern sites. Finally, the
authors would like to kindly thank the dedicated efforts of many other people
at the sampling sites and in the laboratories for collecting and analyzing
the samples. The authors would like to thank the editor and several anonymous
referees for comments that greatly improved the manuscript.

The contribution of primary biogenic organic aerosols to PM is barely documented. This work provides a broad overview of the spatiotemporal evolution of concentrations and contributions to OM of dominant primary sugar alcohols and saccharides for a large selection of environmental conditions in France (28 sites and more than 5 340 samples). These chemicals are ubiquitous, and are associated with coarse aerosols. Their concentrations display site-to-site and clear seasonal variations.

The contribution of primary biogenic organic aerosols to PM is barely documented. This work...